Cardiac arrest is one of the most dynamic pathophysiologic events in clinical medicine. An immediate cascade of pathologic processes is triggered secondary to the abrupt cessation of oxygen delivery. Since oxygen is not stored in sufficient quantities in the body, interruption of adequate oxygen transport to the cells for brief periods of time can result in death. Advanced cardiac life support (ACLS) attempts to provide oxygen delivery ad thereby attenuate this cascade. Rapid and substantial improvement in oxygen delivery is required to decrease the morbidity and mortality of ischemic organ injury. Current monitoring techniques used in ACLS include continuous electrocardiographic monitoring and physical examination e.g. palpation of the carotid or femoral pulse. Both of these techniques provide little information regarding hemodynamic status and oxygen delivery to the brain or body.
Clinical monitoring techniques used as prognostic and therapeutic indicators during ACLS include the coronary perfusion pressure (CPP) or aortic to right atrial relaxation phase pressure gradients, and end-tidal carbon dioxide concentration (ETC02). The importance of CPP as a prognostic indicator of return of spontaneous circulation (ROSC) during animal and human CPR is well established. CPP is the "gold" standard for measuring hemodynamic response to therapy during CPR. Calculation of CPP requires placement of both an aortic artery and central venous catheter which may limit its applicability. ETC02 has been studied in animals and humans and has been proposed as a prognostic and therapeutic guide during CPR. Although ETC02 has the advantage of being non-invasive, it is influenced by multiple variables (i.e. aspiration, pre-existing pulmonary disease) that may limit its reflection of blood flow and CPP in the setting of cardiac arrest. Scv02 monitoring in accordance with the present invention requires only central venous cannulation while Ao-Ra requires venous and arterial cannulation. Scv02 monitoring is not affected by the same extrinsic variables that affect ETC02.
Mixed venous blood reflects tissue oxygen (02) delivery during cardiac arrest-and-circulatory failure. Selective venous hypoxemia or low oxygen content when compared to arterial blood are characteristic during cardiac arrest. Intermittent mixed venous oxygen saturation measurement during ACLS predicts outcome in cardiac arrest patients and hemodynamically unstable trauma patients. In studies made in accordance with the invention, patients successfully resuscitated had higher central venous oxygen saturations than non-resuscitated patients. As far as the present invention is aware, this is the first measurement of this parameter continuously in cardiac arrest patients with fiberoptic technology.
Ideally, mixed venous blood should be drawn from a pulmonary artery catheter. However, placement of such a catheter is unlikely during cardiac arrest. A number of studies have supported the substitution of central venous (right arterial or superior vena cava) blood for mixed venous blood (pulmonary arterial) during spontaneous circulation, circulatory failure and closed chest ACLS. There is reported no significant difference between pulmonary artery, central and femoral venous blood gases during closed chest ACLS in animals.
The catheter in accordance with the invention and methods using the catheter utilize the concept of Scv02. The information provided by such a catheter is a guide to the care of patients in cardiac arrest. It is believed that this is the first utilization of a catheter of this type in this clinical situation. The present invention includes a catheter and methods specific for utilization in cardiopulmonary resuscitation.